Method for introducing impurities

ABSTRACT

To provide an impurity introducing method which can repeatedly carry out such a process that plasma irradiation for realization of amorphous and plasma doping were combined, in such a situation that steps are simple and through-put is high, without destroying an apparatus. 
     At the time of switching over plasmas which are used in plasma irradiation for realization of amorphous and plasma doping, electric discharge is stopped, and an initial condition of a matching point of a high frequency power supply and a peripheral circuit is reset so as to adapt to plasma which is used in each step, or at the time of switching, a load, which is applied to the high frequency power supply etc., is reduced by increasing pressure and decreasing a bias voltage.

TECHNICAL FIELD

This invention relates to a method of introducing impurities, and moreparticularly, relates to a method of forming a junction for forming anelectronic element on a semiconductor substrate, and a method of forminga junction for forming an electronic element on such a substrate that asemiconductor thin film is formed on an insulating substrate surfacewhich is used for a liquid crystal panel etc.

BACKGROUND ART

For example, on the occasion of forming an element region on asemiconductor substrate, a lot of pn junctions are used. In addition,such a SOI (silicon on insulator) substrate that a silicon thin film isformed on a substrate surface through an insulating film is widely usedfor various semiconductor devices such as DRAM. In addition, such aglass substrate that a semiconductor thin film is formed on a substratesurface attracts attention with planning for miniaturization andrealization of high speed of a liquid crystal panel by integrating aliquid crystal drive circuit including thin film transistors (TFTs) inthis semiconductor thin film.

On the occasion of forming various semiconductor devices in this manner,pn junctions are used. As the suchlike method of forming pn junctions, amethod of introducing p type impurities such as boron by ionimplantation into a n type silicon substrate and thereafter,electrically activating them by a halogen lamp, is used conventionally.

For example, as a method of introducing boron which is a p typeimpurity, plasma doping is expected as a next generation method whichcan introduce particles effectively with very low energy, in addition toion implantation.

As a method of electrically activating introduced ions such as boronions, a method of irradiating xenon flash lamp light, all solid-statelaser light, and excimer laser right, other than halogen lamp light, andthe like have been researched and developed.

Here, a method of forming a shallow activated layer by utilizing adifference of optical absorption coefficients of silicon crystal andamorphous silicon has been proposed. In sum, an optical absorptioncoefficient of amorphous silicon is larger as compared with that ofsilicon crystal, in a wavelength range of 375 nm or more. Then, forexample, an amorphous layer is formed in advance on a silicon substratesurface prior to irradiating light, and after that, light is irradiated,and thereby, a lot of light energy is let absorbed by the amorphouslayer, to form a shallow activated layer. In these reports, it isgeneral that realization of pre-amorphous of a substrate surface iscarried out, prior to introduction of impurities, and after that,impurities are introduced. Ion implantation of germanium and silicon isused for the realization of pre-amorphous (see, Non-Patent Documents 1,2, 3, 4, 5 and Patent Document 1).

In recent days, such a process that changing a silicon very shallowlayer to amorphous by use of plasma, and plasma doping were combined,has been proposed by inventors of this case. According to this, plasmasuch as helium is irradiated to a silicon substrate by use of a plasmairradiation apparatus, and thereby, amorphous of a very shallow layer ona silicon surface can be realized. Further, plasma doping is carried outby plasma of gas including boron through the use of the same apparatus,and thereby, very low impurity introduction can be carried out. In thismethod, low energy plasma is used, and therefore, there is such anadvantage that it is possible to realize amorphous of a very low regioneffectively, as compared with ion implantation. Further, by using itwith plasma doping at the same time, it is possible to easily form avery low impurity layer which is changed to amorphous, by 1 unit of theapparatus.

Non-Patent Document 1: Ext. Abstr. Of IWJT, pp23-26, Tokyo, 2002.

Non-Patent Document 2: Symposium on VLSI Technology Digest of TechnicalPapers, pp 53-54, Kyoto, 2003.

Non-Patent Document 3: Ext. Abstr. Of IWJT, pp31-34, Tokyo, 2002.

Non-Patent Document 4: Ext. Abstr. Of IWJT, pp27-28, Tokyo, 2002.

Non-Patent Document 5: 2000 International Conference on Ion ImplantationTechnology Proceedings, 2000, pp.175-177.

Patent Document 1: U.S. Pat. No. 3,054,123 (P3054123)

DISCLOSURE OF THE INVENTION

<Problem that the Invention is to Solve>

In such a process that changing to a silicon very shallow layer toamorphous by use of plasma, and plasma doping were combined, it isdesirable to realize changing to amorphous and plasma doping in the samechamber, from viewpoints of anti-oxidation and anti-pollution of asurface.

In addition, also in the aspect of the apparatus, in case of separatingprocesses and carrying out them by separate plasma irradiationapparatuses, a plurality of chambers are required, and time, which isrequired for delivery between chambers, becomes necessary, and from thatviewpoint, there is such a problem that it is not effective.

Then, various experiments were made repeatedly as to an apparatus whichrealizes such a process that changing a silicon very shallow layer toamorphous by use of plasma, and plasma doping were combined, in the samechamber. In consequence, in the conduct of experiments, it was foundthat there occurs breakage in a power supply and a peripheral circuit ofa plasma introduction apparatus at the time of switching over plasmaswhich are used in both processes.

Furthermore, it was recognized that its cause is because matching pointsof a high frequency power supply and a peripheral circuit, as biasapplication means and a plasma source are different since differentkinds of plasmas are used continuously in a process of continuouslycarrying out a change to amorphous and plasma doping, and a load isapplied at the time of switching over plasma.

In this manner, in case of realizing a change to amorphous and plasmadoping in the same chamber, there was such a problem that a load isapplied to a high frequency power supply or its peripheral circuit asbias application means and a plasma source, at the time of switchingover plasmas, and an apparatus is damaged easily.

In the suchlike situation, provision of method which does not provokebreakage of a high frequency generation source or its peripheralcircuit, at the time of switching over plasma which is used for a changeto amorphous, and plasma which is used for plasma doping, withoutsubstantially dropping down efficiency of an entire process andinvestment efficiency to the apparatus, has been requested.

The present invention is made in view of the above-described actualcondition, and aims to provide a method which can realize a change of asilicon very shallow layer to amorphous by use of plasma, and plasmadoping in the same chamber, without inviting breakage of the apparatus.

<Means for Solving the Problem>

Then, in a method of the present invention, electric discharge isstopped at the time of switching over plasmas between processes ofplasma irradiation for realization of amorphous and plasma doping, andan initial condition of a high frequency power supply as a plasmaapplication or plasma source, or an initial condition of a matchingpoint of a matching circuit is re-set up, so as to adapt to plasma whichis used in each process.

An impurity introducing method of the present invention includes a firstplasma irradiation step of carrying out plasma irradiation forrealization of amorphous in which a surface of a semiconductor substrateis changed to an amorphous situation, and a second plasma irradiationstep of carrying out plasma doping impurities so as to form a shallowjunction in the semiconductor substrate, and includes a resetting stepof resetting a plasma irradiation condition, on the occasion of shiftingfrom the first plasma irradiation step to the second plasma irradiationstep.

By this method, it is possible to prevent an extra load from beingapplied to an apparatus, and effective use becomes possible, andtherefore, it is possible to prevent breakage of the apparatus frombeing provoked.

In addition, in the impurity introducing method of the presentinvention, the resetting step includes a step of resetting an initialcondition of a plasma generation source so as to adapt to plasma whichis used in each step.

By this method, it is possible to easily provide an appropriate plasmasituation.

In addition, in the impurity introducing method of the presentinvention, the resetting step includes a step of resetting an initialcondition of a matching point of a matching circuit so as to adapt toplasma which is used in each step.

By this method, the matching circuit is set up to a matching situationright after plasma irradiation start, and therefore, it is possible toprevent an extra load from being applied to the apparatus.

In addition, in the impurity introducing method of the presentinvention, the resetting step includes a step of stopping electricdischarge once and then, resetting it, on the occasion of shifting fromthe first plasma irradiation step to the second plasma irradiation step.

There is such a case that a large electric current flows at the time ofswitching, but by stopping electric discharge once, it is possible toprevent failure of a high frequency power supply due to matching faultof a matching circuit.

In addition, in the impurity introducing method of the presentinvention, the resetting step includes a step of decreasing and changingbias power and thereafter, applying desired bias power, on the occasionof shifting from the first plasma irradiation step to the second plasmairradiation step.

By this method, there is such a case that a large electric current flowsat the time of switching, but since it is configured so as to lower andchange bias power and thereafter, to apply desired bias power, it ispossible to prevent failure of a high frequency power supply due tomatching fault of a matching circuit. It is desirable to lower biaspower at the time of plasma switching, to 5-50% of bias power to beapplied after switching. More desirably, it is lowered to 5-30%. If itis 50% or more, an advantage is low. On the one hand, if bias power islowered too much, it is not possible to make reflected waves zero.

In addition, in the impurity introducing method of the presentinvention, the resetting step includes a step includes one of decreasingpressure and changing other conditions except pressure, and thereafter,setting desired pressure, on the occasion of shifting from the firstplasma irradiation step to the second plasma irradiation step.

By resetting conditions in such a situation that pressure was lowered,it is possible to shift to the second plasma irradiation step while amatching circuit maintains a matching situation, and therefore, it ispossible to prevent failure of a peripheral circuit and a high frequencypower supply. Pressure at the time of plasma switching is set to 1.1-3.0times of pressure which is set up after switching. If it is 1.1 times orless, there is no advantage. On the one hand, if pressure is increasedto 3.0 times or more, it takes too much time for the process.

In addition, the impurity introducing method of the present inventionincludes a thing characterized in that the second plasma irradiationstep is carried out after the first plasma irradiation step.

In this case, especially, there is a problem of failure due to increaseof loads to a matching circuit and a high frequency power supply at thetime of switching over the plasma irradiation steps, but by using thismethod, it is possible to prevent extra loads to the matching circuitand the high frequency power supply, and to provide an appropriateplasma situation in the second plasma irradiation step. By doing in thismanner, it is possible to obtain such advantages that an advantage forchanging to amorphous, i.e., an optical absorption rate at the time ofannealing is improved, and to enable annealing at low temperature and anactivation rate of impurities are improved, to realize low resistance.In this manner, a device at the time of switching plasmas in such anewly proposed process that plasma irradiation for realization ofamorphous and plasma doping were combined, is very useful.

In addition, the impurity introducing method of the present inventionincludes a thing characterized in that the first plasma irradiation stepis carried out after the second plasma irradiation step.

In this case, especially, there is a problem of failure due to increaseof loads to a matching circuit and a high frequency power supply at thetime of switching over the plasma irradiation steps, but by using thismethod, there is such an advantage that it is possible to preventfailure of a peripheral circuit and a high frequency power supplywithout applying extra loads to the matching circuit and the highfrequency power supply. In this manner, in a device at the time ofswitching plasmas in combination of a step of carrying out plasmairradiation for realization of amorphous after plasma doping is carriedout, so-called step including realization of amorphous aspost-processing, the amorphous realization as post-processing may berealized by ion implantation.

In addition, the impurity introducing method of the present invention isconfigured in such a manner that the first plasma irradiation step iscarried out prior to the second plasma irradiation step.

In this case, especially, there is a problem of failure due to increaseof loads to a matching circuit and a high frequency power supply at thetime of switching over the plasma irradiation steps, but by using thismethod, there is such an advantage that it is possible to preventfailure of a peripheral circuit and a high frequency power supplywithout applying extra loads to the matching circuit and the highfrequency power supply.

In addition, in the impurity introducing method of the presentinvention, gas seed, which is used in the first plasma irradiation step,includes helium and neon.

It is conceivable that helium and neon are of low spattering efficiency,and it is possible to change them to amorphous without almost chippingoff silicon, and it is more desirable.

In addition, in the impurity introducing method of the presentinvention, gas seed, which is used in the second plasma irradiationstep, includes at least one of a group comprising Ar, Kr, Xe, and Rn.

Its reason is that these elements are rare gas, and have acharacteristic of inertness.

In addition, there are a lot of reports in which B₂H₆, BF₃ are used as agas seed which is used in plasma doping, and by combining with theseplasma doping, it is applicable.

In this manner, it is possible to reduce a load which is applied to ahigh frequency power supply etc. at the time of switching of plasmas,and it is possible to carry out such a process that changing to asilicon very shallow layer to amorphous by use of plasma, and plasmadoping were combined, effectively without provoking failure of anapparatus.

In addition, the impurity introducing method of the present invention iscarried out by combination of steps selected from a group comprisingcombination of carrying out plasma doping after plasma irradiation forrealization of amorphous was carried out, combination of carrying outplasma irradiation for realization of amorphous after plasma doping wascarried out, and combination of carrying out plasma doping after plasmairradiation for realization of amorphous was carried out, and afterthat, of further carrying out plasma irradiation for realization ofamorphous.

<Advantage of the Invention>

As explained above, in the present invention, a process is devised so asfor a load not to be applied to a high frequency power supply and acircuit at the time of switching over plasmas, in such a process thatchanging a silicon very shallow layer to amorphous, and plasma dopingwere combined. That is, at the time of plasma switching, by stoppingelectric discharge and setting a matching point so as to adapt to eachplasma, and by decreasing bias power and increasing pressure, it ispossible to carry out the process without destroying a high frequencypower supply and a peripheral circuit.

Therefore, it becomes possible to provide a method of forming a veryshallow impurity introduced layer with a high optical absorption rate,over keeping through-put and investment efficiency to an apparatus, to agood level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view which shows one example of a process in an embodimentof the present invention.

FIG. 2 is a view which shows one example of a process in an embodimentof the present invention.

FIG. 3 is a view which shows one example of a process in an embodimentof the present invention.

FIG. 4 is a view which shows one example of a process in an embodimentof the present invention.

FIG. 5 is a view which shows one example of a process in an embodimentof the present invention.

FIG. 6 is a view which shows one example of a process as a comparativeexample.

FIG. 7 is a view which shows an impurity introducing apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be explained.

Firstly, an apparatus, which is used in this embodiment, will beexplained. In this regard, however, the present invention is not limitedto the following apparatus.

This apparatus 100 has a high frequency power supply 1, a matching box2, a coil and antenna 3, mass flow controllers 4 and 5, a turbomolecular pump 6, a conductance valve 7, a dry pump 8, a circulator 9, aDC power supply 10, a matching box 11, a high frequency power supply 12and a lower electrode 14, and a base body to be processed 13 such as asilicon substrate is placed on the lower electrode 14 which is also usedas a substrate mounting base.

Firstly, a silicon substrate 13 as a substrate to be processed, isconveyed into a process chamber 15, and thereafter, it is disposed onthe lower electrode 14, and an introduction tube 16 of rage gas and anintroduction tube 17 of diborane gas are connected to the processchamber 15 separately. The rage gas is a thing which is used forprocessing for changing a silicon substrate surface to amorphous byirradiating rage gas plasma. It is configured that a gas flow rate canbe controlled by the mass flow controllers 4, 5, separately.

Meanwhile, in this embodiment, changing a surface of a solid base bodyitself to amorphous will be explained, but in this regard, however, thepresent invention is not limited to it, and it is needless to say thatit is also applicable to a surface of a thin film which is formed on thesolid base body.

Embodiment 1

FIG. 1 shows a flow chart of a method of an embodiment 1. In thisembodiment 1, (A) plasma is used in plasma irradiation for realizationof amorphous. In addition, (B) plasma is used in plasma doping. (A)plasma is He plasma, and pressure was set to 0.9 Pa, and bias power wasset to 100 W. (B) plasma is plasma in which B₂H₆ gas is diluted with Hegas, and pressure was set to 2.0 Pa, and bias power was set to 100 W.

In the beginning, an initial condition of a bias high frequency powersupply was set up to a matching point for use in (A) plasma. After that,plasma was irradiated to a silicon substrate by use of (A) plasma, andit was changed to amorphous. After plasma irradiation was carried outonly for predetermined time, plasma was stopped once. Then, an initialcondition of the bias high frequency power supply was set up to amatching point for use in (B) plasma. After that, plasma doping wasapplied to the silicon substrate by use of (B) plasma.

Embodiment 2

FIG. 2 shows a flow chart of a method of an embodiment 2. In thisembodiment 2, (A) plasma is used in plasma irradiation for realizationof amorphous. In addition, (B) plasma is used in plasma doping. (A)plasma is He plasma, and pressure was set to 0.9 Pa, and bias power wasset to 100 W. (B) plasma is plasma in which B₂H₆ gas is diluted with Hegas, and pressure was set to 2.0 Pa, and bias power was set to 100 W.

In the beginning, an initial condition of a bias high frequency powersupply was set up to a matching point for use in (A) plasma. After that,plasma was irradiated to a silicon substrate by use of (A) plasma, andit was changed to amorphous. After plasma irradiation was carried outonly for predetermined time, bias power was lowered to 0 W. After that,a pressure adjustment value was squeezed, and B₂H₆ gas was introducedinto the processing chamber to have pressure increased up to 2.0 Pa, andit was switched over to (B) plasma. After that, bias power is increasedto 100 W, and plasma doping was carried out.

Embodiment 3

FIG. 3 shows a flow chart of a method of an embodiment 3. In thisembodiment 3, (A) plasma is used in plasma irradiation for realizationof amorphous. In addition, (B) plasma is used in plasma doping. (A)plasma is He plasma, and pressure was set to 0.9 Pa, and bias power wasset to 100 W. (B) plasma is plasma in which B₂H₆ gas is diluted with Hegas, and pressure was set to 2.0 Pa, and bias power was set to 100 W.

In the beginning, an initial condition of a bias high frequency powersupply was set up to a matching point for use in (A) plasma. After that,plasma was irradiated to a silicon substrate by use of (A) plasma, andit was changed to amorphous. After plasma irradiation was carried outonly for predetermined time, pressure was increased up to 2.5 Pa, andB₂H₆ gas was introduced into the process chamber, to switch to (B)plasma. After that, pressure was lowered down to 2.0 Pa, and plasmadoping was carried out.

Embodiment 4

FIG. 4 shows a flow chart of a method of an embodiment 4. In thisembodiment 4, (A) plasma is used in plasma irradiation for realizationof amorphous. In addition, (B) plasma is used in plasma doping. (A)plasma is He plasma, and pressure was set to 0.9 Pa, and bias power wasset to 100 W. (B) plasma is plasma in which B₂H₆ gas is diluted with Hegas, and pressure was set to 2.0 Pa, and bias power was set to 100 W.

In the beginning, an initial condition of a bias high frequency powersupply was set up to a matching point for use in (B) plasma. After that,plasma doping was applied to a silicon substrate by use of (B) plasma.After plasma doping was carried out only for predetermined time, plasmawas stopped once. Then, an initial condition of the bias high frequencypower supply was set up to a matching point for use in (A) plasma. Afterthat, plasma irradiation for realization of amorphous was carried out byuse of (A) plasma.

Embodiment 5

FIG. 5 shows a flow chart of a method of an embodiment 5. In thisembodiment 5, (A) plasma is used in plasma irradiation for realizationof amorphous prior to doping. In addition, (C) plasma is used in plasmairradiation for realization of amorphous after doping. Further, (B)plasma is used in plasma doping. (A) plasma is He plasma, and pressurewas set to 0.9 Pa, and bias power was set to 100 W. In this embodiment5, The same thing as (A) plasma is used as (C) plasma. In this regard,however, it is all right even if another condition is used. (B) plasmais plasma in which B₂H₆ gas is diluted with He gas, and pressure was setto 2.0 Pa, and bias power was set to 100 W.

In the beginning, an initial condition of a bias high frequency powersupply was set up to a matching point for use in (A) plasma. After that,plasma was irradiated to a silicon substrate by use of (A) plasma, andit was changed to amorphous. After plasma irradiation was carried outonly for predetermined time, plasma was stopped once. Then, an initialcondition of the bias high frequency power supply was set up to amatching point for use in (B) plasma. After that, plasma doping wasapplied to the silicon substrate by use of (B) plasma. After plasmadoping was carried out for predetermined time, plasma was stopped once.Then, an initial condition of the bias high frequency power supply wasset up to a matching point for use in (C) plasma. Here, since the samething as (A) plasma is used as (C) plasma, a matching point was set upto the same one. After that, plasma irradiation for realization ofamorphous was carried out by use of (C) plasma.

By doing as shown in these embodiments 1 through 5, it became possibleto carry out such a process that irradiation for realization ofamorphous and plasma doping were combined, repeatedly, withoutdestroying the bias high frequency power supply. By this means, itbecame possible to easily fabricate a very shallow impurity layer havinga high optical absorption rate, without destroying the apparatus.

COMPARATIVE EXAMPLE

Next, a comparative example will be explained.

By use of FIG. 6, a difference of processes in the embodiments and thecomparative example will be explained.

In the comparative example, (A) plasma is used in plasma irradiation forrealization of amorphous, and (B) plasma is used in plasma doping. (A)plasma is He plasma, and pressure was set to 0.9 Pa, and bias power wasset to 100 W. (B) plasma is plasma in which B₂H₆ gas is diluted with Hegas, and pressure was set to 2.0 Pa, and bias power was set to 100 W.

In the comparative example, in the beginning, an initial condition of abias high frequency power supply was set up to a matching point for usein (A) plasma. After that, plasma was irradiated to a silicon substrateby use of (A) plasma, and it was changed to amorphous. After plasmairradiation was carried out only for predetermined time, B₂H₆ gas wasintroduced into a process chamber, and pressure was adjusted to be setto 2.0 Pa, and plasma doping was applied to the silicon substrate by useof (B) plasma. Although it was tried to adjust a matching point of biasautomatically at the time of switching of plasmas at this time, a loadis applied to the bias high frequency power supply at an initial stageof starting adjustment, and the bias high frequency power supply breaksdown often times. The number of faults was 3 times during a period of 6months.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, it is possibleto repeatedly carry out such a process that plasma irradiation forrealization of amorphous and plasma doping were combined, in such asituation that steps are simple and through-put is high, withoutdestroying a bias high frequency power supply, and it is possible toeasily fabricate a very shallow impurity layer having a high opticalabsorption rate, and therefore, it is useful for formation of a finesemiconductor integrated circuit.

1. An impurity introducing method, including a first plasma irradiationstep of carrying out plasma irradiation for realization of amorphous inwhich a surface of a semiconductor substrate is changed to an amorphoussituation, and a second plasma irradiation step of carrying out plasmadoping impurities so as to form a shallow junction in the semiconductorsubstrate, and including a resetting step of resetting a plasmairradiation condition, on the occasion of shifting from the first plasmairradiation step to the second plasma irradiation step, wherein theresetting step includes a step of resetting an initial condition of aplaten RF power supply system so as to adapt to plasma which is used ineach step.
 2. The impurity introducing method as set forth in claim 1,wherein the resetting step includes a step of resetting an initialcondition of a matching point of a matching circuit so as to adapt toplasma which is used in each step.
 3. The impurity introducing method asset forth in claim 1, wherein the resetting step includes a step ofelectric discharge once and then, resetting it, on the occasion ofshifting from the first plasma irradiation step to the second plasmairradiation step.
 4. The impurity introducing method as set forth inclaim 1, wherein the resetting step includes a step of decreasing biaspower and thereafter, applying desired bias power, on the occasion ofshifting from the first plasma irradiation step to the second plasmairradiation step.
 5. The impurity introducing method as set forth inclaim 1, wherein the resetting step includes a step of decreasingpressure and changing other conditions except pressure, and thereafter,setting desired pressure, on the occasion of shifting from the firstplasma irradiation step to the second plasma irradiation step.
 6. Theimpurity introducing method as set forth in claim 1, characterized inthat the second plasma irradiation step is carried out after the firstplasma irradiation step.
 7. The impurity introducing method a set forthin claim 6, wherein it is configured in such a manner that the firstplasma irradiation step is carried out after the second plasmairradiation step.
 8. The impurity introducing method as set forth inclaim 1, wherein it is configured in such a manner that the first plasmairradiation step is carried out prior to the second plasma irradiationstep.
 9. The impurity introducing method as set forth in claim 1,characterized in that gas seed, which is used in the first plasmairradiation step, includes helium or neon.
 10. The impurity introducingmethod as set forth in claim 1, wherein gas seed, which is used in thesecond plasma irradiation step, includes at least one of a groupcomprising Ar, Kr, Xe, and Rn.